Pipelines are used extensively for conveying liquids. One area where pipelines are used is in the transporting of liquid from bulk storage tanks. Many types of liquids are stored in bulk, both above ground and underground. A special problem exists with leaks in the pipelines used in connection with underground storage tanks. If the liquid being conveyed is a danger to the environment or the health when not controlled, substantial damage can occur before the leak is even detected. A good example of this are the pipelines used to convey liquid gasoline at retail gasoline service stations. Necessarily, these stations are in populated areas and therefore there is always a danger associated with leaks from the tanks or pipelines associated therewith.
Leaked gasoline poses a hazard to the environment as well as an obvious health hazard. Any leak which develops is normally very slow initially. This means that the leak is difficult to detect until a substantial amount of gasoline has leaked. By that time environmental damage and possible health problems have occurred.
Various attempts have been made to alleviate the problems associated with underground pipelines, including use of double walled pipeline systems. In this type of system, an outer pipeline wall acts as a containment vessel if an inner pipeline wall develops a leak. A slow leak in the pipeline is satisfactorily contained. However, installation of known double walled pipelines is difficult. Initially there can be a problem of getting the inner pipeline inside of the outer pipeline. This is especially true for long lengths of pipelines wherein the inner pipeline is flexible. Even a semi-rigid inner pipeline is difficult to work with due to the fact it is normally wound on a reel in manufacturing. The curved nature of the pipeline stored and shipped in this manner tends to persist.
Another problem experienced with double wall pipeline systems is the need for special fittings normally needed with any pipeline system. Straight fittings, elbows and T-fittings are often used in connecting a pipeline terminal to another pipeline terminal, dispenser, etc. Known fittings used on conventional single wall pipelines are not able to maintain a segregation of the inner pipeline flow channel from the outer pipeline flow channel. The lack of reliable easy to use fittings for use on double wall pipeline systems has reduced the attractiveness of such systems.
There has now been developed double wall fittings for double wall pipeline systems. The fittings solve many of the problems inherent with the existing fitting systems. The fittings of this invention are economical and provide a means of connecting not available previously.